Apparatus and Method for Transmitting and Receiving Data

1. An apparatus for transmitting data, the apparatus comprising: a first symbol mapper configured to generate a plurality of key symbols by performing symbol mapping on information about an optimum key index that instructs a modified Walsh-Hadamard matrix that causes a minimum peak-to-average power ratio (PAPR); a first modified Walsh-Hadamard transformer configured to generate a plurality of modified Walsh-Hadamard-transformed data symbols by performing modified Walsh-Hadamard transform on a plurality of data symbols according to a modified Walsh-Hadamard matrix that the optimum key index instructs; an inverse Fourier transformer configured to generate a plurality of inverse Fourier-transformed symbols by performing inverse Fourier transform on the plurality of key symbols and the plurality of modified Walsh-Hadamard-transformed data symbols; and a transmitter configured to transmit the plurality of inverse Fourier-transformed symbols to a channel through at least one antenna.

2. The apparatus of claim 1 , wherein the information about the optimum key index corresponds to an optimum search key index, and the optimum key index is obtained by a search interval and the optimum search key index.

3. The apparatus of claim 2 , further comprising an optimum key index generator configured to generate the optimum key index.

4. The apparatus of claim 3 , wherein the optimum key index generator comprises: a key index generator configured to generate a present key index corresponding to a present search key index; a second modified Walsh-Hadamard transformer configured to generate a plurality of modified Walsh-Hadamard-transformed search data symbols by performing modified Walsh-Hadamard transform on the plurality of data symbols according to a modified Walsh-Hadamard matrix that the present key index instructs; a second symbol mapper configured to generate a plurality of search key symbols by performing symbol mapping on the present search key index; an inverse Fourier transformer configured to generate a plurality of inverse Fourier-transformed symbols by performing inverse Fourier transform on the plurality of search key symbols and the plurality of modified Walsh-Hadamard-transformed search data symbols; a measuring unit configured to measure a PAPR of the plurality of inverse Fourier-transformed symbols; and a minimum PAPR detector configured to determine an optimum search key index or an optimum key index corresponding to a minimum PAPR of PAPRs corresponding to a plurality of search key indexes.

5. The apparatus of claim 4 , wherein the optimum key index generator further comprises: a key combination vector generator configured to generate a present key combination vector corresponding to the present key index; and a modified Walsh-Hadamard matrix generator configured to generate a modified Walsh-Hadamard matrix according to the present key combination vector.

6. The apparatus of claim 5 , wherein the key combination vector generator generates the present key combination vector corresponding to the present key index from a table that defines a relationship between a key index and a key combination vector.

7. The apparatus of claim 6 , wherein the key combination vector generator generates the present key combination vector corresponding to the present key index using a key combination vector generation algorithm that receives the present key index as an input.

8. The apparatus of claim 4 , wherein the second modified Walsh-Hadamard transformer generates the plurality of modified Walsh-Hadamard-transformed search data symbols by grouping the plurality of data symbols into a plurality of data symbol groups and by performing modified Walsh-Hadamard transform on each data symbol group.

9. A method of transmitting data in a data transmission apparatus, the method comprising: generating a plurality of key symbols by performing symbol mapping on information about an optimum key index that instructs a modified Walsh-Hadamard matrix that causes a minimum PAPR; generating a plurality of modified Walsh-Hadamard-transformed data symbols by performing modified Walsh-Hadamard transform on a plurality of data symbols according to a modified Walsh-Hadamard matrix that the optimum key index instructs; generating a plurality of inverse Fourier-transformed symbols by performing inverse Fourier transform on the plurality of key symbols and the plurality of modified Walsh-Hadamard-transformed data symbols; and transmitting the plurality of inverse Fourier-transformed symbols to a channel through at least one antenna.

10. The method of claim 9 , wherein the information about the optimum key index corresponds to an optimum search key index, and the optimum key index is obtained by a search interval and the optimum search key index.

11. The method of claim 10 , further comprising generating the optimum key index.

12. The method of claim 11 , wherein generating the optimum key index comprises: generating a present key index corresponding to a present search key index; generating a plurality of modified Walsh-Hadamard-transformed search data symbols by performing modified Walsh-Hadamard transform on the plurality of data symbols according to a modified Walsh-Hadamard matrix that the present key index instructs; generating a plurality of search key symbols by performing symbol mapping on the present search key index; generating a plurality of inverse Fourier-transformed symbols by performing inverse Fourier transform of the plurality of search key symbols and the plurality of modified Walsh-Hadamard-transformed search data symbols; measuring a PAPR of the plurality of inverse Fourier-transformed symbols; and determining an optimum search key index or an optimum key index corresponding to a minimum PAPR of PAPRs corresponding to a plurality of search key indexes.

13. An apparatus for receiving data, the apparatus comprising: a receiver configured to receive a plurality of digital symbols from a channel through at least one antenna; a Fourier transformer configured to generates a plurality of Fourier-transformed key symbols and a plurality of Fourier-transformed data symbols by performing Fourier transform on the plurality of digital symbols; an optimum key index generator configured to generate an optimum key index from the plurality of Fourier-transformed key symbols; a modified inverse Walsh-Hadamard transformer configured to generate a plurality of modified inverse Walsh-Hadamard-transformed data symbols by performing modified inverse Walsh-Hadamard transform on the plurality of Fourier-transformed data symbols according to a transposed matrix of a modified Walsh-Hadamard matrix that the optimum key index instructs; and a symbol mapper configured to convert the plurality of modified Walsh-Hadamard-transformed data symbols to a plurality of binary data signals.

14. The apparatus of claim 13 , wherein the optimum key index generator generates an optimum search key index from the plurality of Fourier-transformed key symbols and generates the optimum key index using a search interval and the optimum search key index.

15. The apparatus of claim 14 , further comprising an optimum key combination vector generator configured to generate an optimum key combination vector corresponding to the optimum key index, wherein a modified Walsh-Hadamard matrix that the optimum key index instructs is generated by changing a position of a row or a column of an original Walsh-Hadamard matrix according to the optimum key combination vector.

16. The apparatus of claim 13 , wherein the modified inverse Walsh-Hadamard transformer generates a plurality of modified inverse Walsh-Hadamard data symbols by grouping the plurality of Fourier-transformed data symbols into a plurality of data symbol groups and by performing modified inverse Walsh-Hadamard transform on each data symbol group.

17. A method of receiving data in a data receiving apparatus, the method comprising: receiving a plurality of digital symbols from a channel through at least one antenna; generating a plurality of Fourier-transformed key symbols and a plurality of Fourier-transformed data symbols by performing Fourier transform on the plurality of digital symbols; generating an optimum key index from the plurality of Fourier-transformed key symbols; generating a plurality of modified inverse Walsh-Hadamard-transformed data symbols by performing modified inverse Walsh-Hadamard transform on the plurality of Fourier-transformed data symbols according to a transposed matrix of a modified Walsh-Hadamard matrix that the optimum key index instructs; and converting the plurality of modified Walsh-Hadamard transformed data symbols to a plurality of binary data signals.

18. The method of claim 17 , wherein generating the optimum key index comprises: generating the optimum search key index from the plurality of Fourier-transformed key symbols; and generating the optimum key index using a search interval and the optimum search key index.

19. The method of claim 18 , further comprising: generating an optimum key combination vector corresponding to the optimum key index; and generating a modified Walsh-Hadamard matrix that the optimum key index instructs by changing a position of a row or a column of an original Walsh-Hadamard matrix according to the optimum key combination vector.

20. The method of claim 17 , wherein generating the plurality of modified inverse Walsh-Hadamard-transformed data symbols comprises: grouping the plurality of Fourier-transformed data symbols into a plurality of data symbol groups; and generating the plurality of modified inverse Walsh-Hadamard-transformed data symbols by performing modified inverse Walsh-Hadamard transform on each data symbol group.